Predicting the Future Climate*
J. Ernest "Sunny" Breeding, Jr., PhD Geophysics
What about Predictions?
Climate science is well understood today. Climate scientists know very well what can happen to the Earth in the future, and it depends on whether we reduce greenhouse gases that are now going into the atmosphere or continue to add greenhouse gases at an ever increasing rate. However, knowing what will happen and when it will happen are two different things. Predicting precisely when something will happen, such as when the sea level will rise by 4 feet (1.2 meters), is difficult for several reasons. For one, it will depend upon the rate at which people will allow carbon dioxide or other greenhouse gases to go into the atmosphere in the future, and that is unknown. Another problem is that we have not been through this before. This is the first time that the Earth has experienced human created global warming. It is not like predicting the path of a hurricane where we have experienced many hurricanes before. With each new hurricane the data is used to check and refine hurricane prediction models. The accuracy in predicting hurricane paths has increased greatly through the years. Some might say "but the Earth has experienced global warming before." That is true, and an example of global warming that occurred through natural processes is on Page 4. The difference between that example and what is happening now is huge, and is one of the difference in timescales. Incidents of global warming that occurred in nature took place over many thousands and even millions of years. The changes occurred very slowly. This allowed animal and plant life time to adjust. Even so, some life forms went extinct. The global warming that we are experiencing today is happening on a time scale of decades or centuries. The changes are too rapid for nature to be able to properly adjust (Hansen, 2009.) That is why it is necessary for man to fix the problem that man created. In making predictions it is now prudent to error on the side of being conservative. The fact that ice on our planet is melting or breaking up faster than had been expected reinforces this conclusion. As more data is analyzed in the coming decades climate scientists will be able to refine their predictions of when things will happen.
How Much Will the Earth Warm in the Future?
As stated above, it is difficult to predict the future warming of the Earth because we do not know how much the rate of adding greenhouse gases to the atmosphere will change. The present situation of continually adding more greenhouse gases is not likely to change until enough people are convinced of the severity of the problem and support lowering dangerous emissions. But even if the emissions of greenhouses gasses stopped today some of the carbon dioxide already in the atmosphere will be there for another century or longer. That is one of the big problems. Also, developing countries like China and India are now creating more greenhouse gases. In fact, China has replaced the United States as the the number one polluter of the atmosphere.
Fig. 6.1. Model predictions of warming due to greenhouse gases. (USGCRP)
Fig. 6.2. Polar bears on Sea Ice. (USGCRP)
We are particularly interested in projections of greenhouse gases for the next 50 to 100 years. Fig. 6.1 shows observations from 1900 to near the present and the model simulation for comparison with the measurements. The model prediction is in good agreement with the observations. In Fig. 6.1 there are also three different predictions of warming to the year 2100 based on different rates of the addition of greenhouse gases to the atmosphere. The lower emissions scenario shows an increase in the global average surface temperature of about 4 degrees fahrenheit (2.2 degrees Centigrade) by the end of the century. That is really a significant increase and will result in much damage if allowed to happen. The other two scenarios show increases of about 7 and 8 degrees Fahrenheit (3.9 and 4.4 degrees Centigrade). Those are very large increases, and will most certainly cause very serious problems to life on Earth.
What is likely to happen in the future?
Global warming will only get worse if we continue to add greenhouse gases to the atmosphere. To get an idea of some of the possible problems we will encounter we will look at some examples. Animal and plant life will be greatly affected. In Fig. 6.2 above the polar bears will be challenged as sea ice will eventually disappear during summer months and perhaps longer. That will make finding food for them very difficult, as they use the sea ice to get to seals. Unless the polar bears can adapt they will become extinct. But similar challenges will exist for many birds, amphibians, reptiles, insects, and other animals, as many of them can only tolerate a limited range of temperature and moisture. Lack of food and water are potential problems for many. Plant life is also vulnerable.
Fig. 6.3. Dry lake. (USGCRP)
Fig. 6.4. City smog (haze). (USGCRP)
Dry lake beds will be common in many areas as droughts become more common. Global warming causes extremes. Areas that are now dry are expected to become larger and get dryer. This will affect many people in the world. The problem areas in places like Africa will get worse. In the United States the Southwest is especially vulnerable. Many cities already have reduced water supplies. Pictures like the one in Fig. 6.3 will become much more common. Unless alternative sources of water are found for homes and irrigation for crops drought stricken areas will seriously challenge people or cease to be livable. The city scene in Fig. 6.4 will become more common leading to heat related deaths and more disease due to the poor quality of the air we breathe.
Fig. 6.5. Intense storm. (USGCRP)
Fig. 6.6. Large ocean waves. (USGCRP)
Storms, like the one pictured in Fig. 6.5, are predicted to be more intense. Areas that are now wet will get larger and wetter. With global warming there is greater evaporation from the warmer bodies of water. At the same time the atmosphere gets warmer and as the air warms it can hold more water vapor, meaning greater amounts of rain. The prediction for hurricanes is interesting. More hurricanes are expected because of the warmer ocean water. But it is also expected that there will be winds at the higher elevations that will prevent some hurricanes from forming. So it is thought that the lower category hurricanes will not occur as often, but that there will be a larger number of the higher category hurricanes. These intense storms will produce large ocean waves as seen in Fig. 6.6. Large storm surges are more likely and because of rising sea level will ride higher and flood even further inland than is possible now.
Fig. 6.7. Hurricane damage due to Katrina and Rita. (USGCRP)
Hurricane damage like that illustrated in Fig. 6.7 is likely to become more common. The before and after pictures are stunning. They show what the offshore regions near New Orleans looked like before and after Hurricanes Katrina and Rita struck in 2005. Both storms became Category 5 hurricanes in the Gulf of Mexico.
Fig. 6.8. Predicted coastal flooding. (USGCRP)
As sea level rises more and more regions will not be livable or useable. Fig. 6.8 shows what could happen on the Gulf Coast near New Orleans if the sea level rises 4 feet (1.2 meters). Based on a medium emission level or greater this is thought very likely to happen within the next 50 to 100 years. Not only will people on the coast be displaced, roads and highways along the coast will be underwater. This problem will occur throughout much of the world in coastal regions. Some islands will no longer be inhabitable. It has been estimated that with a 1 meter (3.28 feet) rise in sea level that 60 million people throughout the world will have to be relocated. Further, many more people will be more vulnerable to storm surges and flooding (Gavin Schmidt in Schmidt and Wolfe, 2009.) These predictions seem even more likely based on recent data that show that not only the Greenland ice sheets but also the Antarctic ice sheets are braking up and melting faster than had been expected.
The Melting of Ice Sheets
It has been discovered that the ice sheets in Antarctica are melting from the bottom as well as the top. The same thing is happening in Greenland. The ocean has been warming and the water is getting under the ice, which rests on rock. Big lakes have been discovered under the ice. The water being warmer than the ice causes the ice to melt. In addition, the water causes the ice to be slippery and some of it can breakup and move ending up as icebergs in the ocean, which causes sea level to rise. See Polar Regions described in a video by Dr. Robin E. Bell and other scientists at the Lamont-Doherty Earth Observatory of Columbia University.
In October 2011 NASA scientists discovered a major ice crack in the Pine Island Glacier which drains the West Antarctic Ice Sheet. The crack is clearly seen in an image taken in November 2011 from a spacecraft and shown in Fig. 6.9. The crack was found to be 260 feet (80 meters) wide and 195 feet (60 meters) deep. The crack will eventually extend all the way across the glacier and calve a very large iceberg with an area of about 350 square miles (900 square kilometers). Note that it is not necessary for the icebergs in the ocean to melt in order for sea level to rise. They only have to move from land to water. This is because as the ice floats it sinks into the water by an amount that displaces its own mass, raising sea level. You see this happen every time you add an ice cube to a glass of water. The same thing is happening with the Greenland ice sheet where an iceberg with an area about the size of the state of Rhode Island calved ending up in the water. Lots of icebergs of all sizes are calving from the ice sheets in Greenland, Antarctica, and other places.
Fig. 6.9. Pine Island Glacier of the West Antarctic Ice Sheet. (NASA/GSFC/METI/ERSDAC/JAROS & U.S./Japan ASTER Science Team)
Sea level is now expected to rise faster than had been expected. Of great concern is that if the ice on land continues to breakup and slip into the oceans a tipping point could eventually be reached where we can no longer stop the disintegration of the ice sheets. That is a frightening possibility as most coastal cities on our planet could be submerged under water. Only those cities on cliffs high enough above the present sea level would be spared flooding. If all of the ice on Earth were to disintegrate or melt and end up in the oceans, sea level would rise by about 250 feet (77 meters) (Hansen, 2009.) There is a lot of ice in Antarctica, and it might take centuries for all of it to melt or breakup, depending on the degree of global warming and how the ice sheets disintegrate. But only a fraction of the ice has to melt or breakup into icebergs to cause very serious damage. Sea level is expected to rise by a significant amount this century as the Earth gets warmer. The only way to stop the rise in sea level is to reduce the greenhouse gases that are in the atmosphere. The longer we wait to do this the more we press our luck.
Carbon Dioxide, Methane, and Gases in the Atmosphere
Based on volume the dry atmosphere (air) is made up mostly of nitrogen at 79.09% and oxygen at 20.95%. At much smaller concentrations are argon at 0.93%, carbon dioxide at 0.0394%, and methane at 0.000179%. Other gases exist, but in very small quantities. Water vapor is very variable throughout the planet, but on average is about 1% of air (Wikipedia, Atmosphere of Earth).
With a concentration of only about 0.0394% (394 ppm) in the Earth's atmosphere Carbon dioxide is clearly a trace gas. Because this concentration is so low some people assume that carbon dioxide cannot be responsible for the current global warming. Nothing could be further from the truth. A statistic that is much more important is that since the Industrial Revolution, in about 1750, the concentration of carbon dioxide in the atmosphere has increased by about 43%. Most of this increase has come since the mid-nineteen hundreds. Carbon dioxide in the Earth's atmosphere is very effective at absorbing infrared radiation emitted from the Earth's surface and then reemitting it. The result is a warming of the Earth's surface, and if there is too much of it the result is global warming. This is the greenhouse effect.
A lot of carbon dioxide is stored in the oceans. As much as one-third of the carbon dioxide going into the atmosphere is currently thought to be absorbed by the oceans. However, since the oceans are getting warmer the amount of carbon dioxide the oceans can take on is decreasing. Further, at some point the oceans can become saturated with carbon dioxide and not absorb any more from the atmosphere. So in the future, it is difficult to predict when, it is likely that a greater percentage of carbon dioxide emissions will end up in the atmosphere, and that is not a good thing as it will add to the global warming (Broecker and Kunzig, 2008.)
Trees and plants are a natural sink for carbon dioxide as they absorb it. But large forest areas are being destroyed for farming or to build cities. That means less carbon dioxide is being absorbed. Further, since the trees are often burned they become a source of carbon dioxide.
Another major worry is methane, which is a naturally occurring greenhouse gas. It comes from organic material that decays in the absence of oxygen and is found in soil and on lake and ocean bottoms. It currently is not as important a greenhouse gas as is carbon dioxide. Methane is also shorter-lived than carbon dioxide. Methane lasts a decade compared to more than a century for carbon dioxide. But by comparison a molecule of methane is about twenty to twenty-five times more powerful as a greenhouse gas than a molecule of carbon dioxide. As the Arctic warms the permafrost is thawing and methane is being released to the atmosphere. There is an enormous amount of methane frozen in the form of methane hydrates. Large quantities are found in the continental shelf regions of the Arctic Ocean and the Gulf of Mexico. Currently the high pressure and the cold temperature of the water where the hydrates are found keep them stable. The fear is that the warming ocean water could be transported by currents and melt the hydrates causing the release of large quantities of methane into the atmosphere. This would greatly increase the global warming of the Earth (Schmidt and Wolfe, 2009.) We could also pass a tipping point, meaning it would be too late for us to stop the process. We need to make sure that this does not happen by reducing the carbon dioxide in the atmosphere.
Fig. 6.10. West Nile Virus. (USGCRP)
Fig. 6.11. Temple at Chichen Itza. (Breeding)
Mosquitoes will thrive in a warmer climate. That means diseases like the West Nile Virus, illustrated in Fig. 6.10, and malaria will become much more pronounced and likely to expand beyond those regions where the deceases are now prevalent.
Climate and Past Civilizations
Fig. 6.11 shows a picture of the main temple at Chichen Itza in Yucatan, Mexico. This is a Mayan Ruin site. I took the picture on a visit there. When you climb the 91 steps to the top you are 82 feet (25 meters) high, and can look out over what was once a thriving city. It and neighboring cities were abandoned in the 1300s. It is now known that climate was the reason due to an intense drought. A number of other cities were abandoned in the past, and it is known that climate was a factor for some. This includes Angkor in Cambodia.
The Impact of Global Warming
If global warming continues unabated there will most certainly be more intense droughts causing devastation on a much greater scale than happened at Chichen Itza or Angkor in previous times, or as seen in Sahel today. Increased flooding is also a problem. Iowa has already had three 100-year floods in 20 years, and there are other examples. Further, sea level will continue to rise eventually displacing many millions of people as well as wildlife. Intense storms including hurricanes and storm surges will add to the problems of mankind.
Some cities, states, and world governments are already making plans to deal with a warmer Earth. For example, Chicago is taking a look at their sewer pipes and flood-control reservoirs, which are not capable of handling the flooding from the more intense rains that are expected in coming years. They have already repaved more than one hundred alleys with porous pavers or pervious concrete so that rainwater can seep into the ground rather than flow into sewers and possibly backup into businesses and homes. With sea level rising ocean waves and storm surges will ride at higher levels and penetrate further inland. This is not good news, especially since more intense storms including high category hurricanes are expected in the future due to a warming Earth. Some governments are making plans for this eventuality. More serious droughts like that currently seen in the southwestern United States are expected in the years ahead. This will lead to dwindling water supplies and a loss of more homes due to area-wide fires caused by dry conditions. More intense tornados are also expected in future years. All of these problems will lead to loss of life and enormous amounts of damage with big expenses for individuals, insurance companies, and all governments including agencies like FEMA in the United States. Can we afford a warmer Earth?
It should be obvious that we must take adequate measures to reduce the greenhouse gas emissions in the atmosphere. We need to examine what we can do to protect and save life on our planet. That is what we will look at next.
Page 1: Climate Change and Definition
Page 2: Evidence of Global Warming
Page 3: Measurements
Page 4: Ice Ages
Page 5: Causes of Climate Change
Page 6: Predicting the Future
Page 7: How Can We Fix Our Climate?
Page 8: References
*A slide show version of these pages on climate change is available for presentations to groups. See References for more details.
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